Rat liver cells and mouse epidermal cells are used for studying the mechanism of chemical carcinogenesis in epithelial cells. A cell line, derived from rat liver and tumorigenically transformed by exposure of the cells in culture to DL-ethionine, serves as a model to determine genetically stable cell modifications due to transformation, particularly those relating to cell-substrate and cell-cell adhesion. The characterization of the ethionine-transformed cell line and its nontransformed control has been achieved and evidence has been presented for 1) the epithelial nature of these cells, 2) their origin from liver epithelium, and 3) the identification of cellular alterations that resulted specifically from ethionine treatment and subsequent transformation. Cytoskeletal arrangements and adhesion characteristics of the transformed liver cells have been compared to those of the nontransformed controls using immunochemistry, reflection contrast and phase microscopy, and electron microscopy. Our results give evidence, in cultures of transformed cells, for an increase in cell-substrate adhesion due to increases in the number of focal contacts and in the expression of fibronectin; concomitantly, a loss of cell-cell adhesion via intermediate junctions is indicated. The changed growth patterns in the transformed cell cultures are thus defined as progressive deficiencies in cell contact interactions. The promotable mouse epidermal cell line, JB6, is subjected to a similar protocol with the goal of characterizing promotion specific events.